Unitised doses of detergents and bleaching compositions have been found to be both attractive and convenient to consumers. Indeed, a “unit dose” is easy to handle and avoids the need of the consumer to measure the product, thereby giving rise to more precise dosing and avoiding wasteful overdosing or under-dosing.
It is often advantageous to utilize multi-compartment pouches. In such pouches incompatible ingredients can be split, or both liquid and solid compositions can be utilized. Some ingredients for instance are more stable in solid form than liquid, and vice versa.
The multicompartment pouch is made of a water-soluble film. This film requires the presence of low molecular weight solvent both in the film (added during manufacture, or casting) and in the liquid composition, to act as a plasticizer. Plasticizers in the film increase the plasticity or fluidity of the film, in other words making it strong and elastic. In the absence of plasticizers, the film is brittle. This ensures uniform thickness of the film during the manufacture of the film and subsequent pouch formation, and prevents it from tearing of splitting during manufacture and shipment/storage.
Low molecular weight solvents, which act as plasticizers in the liquid composition, are necessary to increase film elasticity, but also to prevent the film from dissolving during the storage in the presence of water (both atmospheric moisture and water in the liquid composition). Pouch films, such as polyvinyl alcohol are sensitive to several compounds, such as strong acids and bases, and oxidizing compounds. There can also be specific film/product interactions which can decrease the solubility. For example carboxylic groups present in some films can react with hydroxyl groups also in the film, in the presence of di-carboxylic acids (such as citric acid) to form intra-molecular lactone rings or inter-molecular esters. This results in the solubility of the film significantly reducing, and the film becoming opaque during storage.
A preferred bleaching agent is an oxygen bleach. When used in conjunction with bleach activators, oxygen bleaches offer excellent cleaning. The oxygen bleach source and the bleach activator are powder ingredients. In the presence of water, the oxygen bleach source and the bleach activator react together to form free oxygen. If this occurs within the enclosed pouch, it could cause the pouch to rupture.
Furthermore, often, the bleach activator is coated with palmitic acid. Palmitic acid is a relatively inert saturated fatty acid. Its presence helps minimise hydrolysis of the bleach activator in the presence of alkaline ingredients in the composition. Reaction between the oxygen bleach source and the bleach activator (caused by the presence of water and/or solvents) can oxidize the palmitic acid. For example, if the oxygen bleach source is peroxide, then peracid is formed that reacts strongly with the palmitic acid. This oxidation of palmitic acid forms a yellow product which causes yellowing of the powder composition.
Moreover, the reaction of the oxygen bleach source and bleach activator in the presence of water, causes plasticization of the film. This is due to the reaction of, for example, peracid with the alcoholic group and acetate sites of the film, destroying the polymer structure.
Interestingly, it was found that the low molecular weight solvent was migrating from the liquid composition into the solid composition and causing the bleach activator to react with the bleach oxygen source. This caused the above mentioned problems and also resulted in overall lower levels of bleaching compounds, thus affected the cleaning efficiency.
Therefore, there is a need to provide multi-compartment pouches comprising an oxygen bleach source and bleach activator, which exhibit improved stability over time.
Surprisingly, the incorporation of a polycarboxylate polymer in the solid composition reduced the amount of low molecular weight solvent migrating from the liquid composition into the solid composition and resulted in reduced bleach activator and oxygen bleach source reaction. This resulted in overall improved compositional and pouch stability over time.